Indicia sensor system for optical reader

ABSTRACT

In the present invention, the control unit of an optical reader analyzes image data being generated by the imaging element of the reader and changes the mode of operation of the reader if the image data indicates that machine readable indicia, such as a bar code symbol or a text character, is likely in the field of view of the reader. Normally, analysis of image data includes the step of detecting for edge transitions in the image information. If the control unit determines that the image data includes more than a predetermined number of edge transitions, then the control unit imparts appropriate control over various reader elements to change the mode of operation of the reader. Normally, the control unit changes the mode of operation of the reader from a first mode, wherein the reader does not operate to decode or recognize image data to a second mode, wherein the reader operates to decode and/or recognize image data.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation of U.S. patent application Ser. No.09/432,282 filed on Nov. 2, 1999 the content of which is relied upon andincorporated herein by reference in its entirety, and the benefit ofpriority under 35 U.S.C. §120 is hereby claimed.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to optical readers in general andparticularly to an optical reader configured to change operating modesdepending on characteristics of images in the reader's field of view.

[0004] 2. Background of the Prior Art

[0005] Prior art optical readers are sometimes configured to operate ina “continuous scan mode” so that bar code symbols and other indiciapresented to the reader are automatically decoded or otherwiserecognized without manually activating a control element such as atrigger to commence indicia recognizing activities.

[0006] A continuous scan operating configuration requires repetitiveillumination flashing of an LED array in the case of an image sensorbased optical reader and repetitive laser scanning in the case of alaser scan engine based optical reader. Repetitive flashing illuminationor laser scanning requires a high level of energy consumption and canresult in premature component degradation. Furthermore, the repetitiveillumination or laser scanning has been observed to be highlydistracting to users of such optical readers configured to continuouslyscan image data.

[0007] U.S. Pat. No. 5,550,366 describes a system for automaticallyactivating image scanning in a portable bar code reader when thepresence of a bar code in a target area is detected. However, thedetection of a bar code in the target area is carried out on a periodbasis and requires for the detection activation of a high radiancesource of illumination. Accordingly, the system is not responsive inreal time to an object being moved into the field of view of the reader,and the high radiance illumination required for operation of the systemremains a source of distraction.

[0008] There is a need for an optical reader which is configured toautomatically and in real time decode or otherwise recognize machinereadable indicia that is presented to the reader without manualactivation of a control element to commence recognition operations.

SUMMARY OF THE INVENTION

[0009] According to its major aspects and broadly stated, the inventionis a method for operating an optical reader so that control of thereader depends on image information being generated by the opticalimaging element, such as an image sensor, of the reader.

[0010] In one embodiment, the reader control unit analyzes imageinformation being generated by the imaging element and changes the modeof operation of the reader if the image information indicates thatmachine readable indicia, such as bar code symbols or a text character,is in the field of view of the reader. Normally, analysis of image dataincludes the step of detecting for edges, or edge transitions in theimage information. If the control unit determines that the imageinformation includes more than a predetermined number of edgetransitions, then the control unit imparts appropriate control overvarious reader elements to change the mode of operation to the reader.

[0011] When the control unit determines that machine readable indicia isin the field of view of the imaging element then the control unit maychange the mode of operation of the reader from a first mode, whereinthe reader does not operate to decode or otherwise recognize machinereadable indicia to a second mode, wherein the reader actively attemptsto decode or otherwise recognize machine readable indicia. The secondmode may be characterized, for example, by an increased illumination ofthe field of view, and/or by the activation or enhancement of decodingalgorithms being operated to process captured image data and/or by theactivation or enhancement of optical character recognition (OCR)algorithms being operated to process captured image data.

[0012] The method may be utilized with any type of optical reader,including a basic hand held bar code reader, a multi functional datacollection unit having a keyboard, display, and imaging element, a scanstand optical reader, or a fixed mount optical reader mounted togenerate image information corresponding to articles which are manuallyor automatically moved across a point of transaction.

[0013] The method may be utilized with an optical reader to supplementor replace the function normally provided by a trigger switch. In mosthand held optical readers a trigger switch is manually depressed tocommence decoding or recognition operations of the reader. An opticalreader programmed in accordance with the invention may commence decodingand/or recognition operations automatically upon the detection ofmachine readable indicia in the field of view of the reader without atrigger being depressed.

[0014] These and other details, advantages and benefits of the presentinvention will become apparent from the detailed description of thepreferred embodiment herein below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The preferred embodiment of the invention will now be described,by way of example only, with reference to the accompanying Figureswherein like members bear like reference numerals and wherein:

[0016]FIG. 1 is a block electrical diagram of an exemplary opticalreading device in which the invention may be incorporated;

[0017] FIGS. 2A-2H show perspective views of exemplary optical readersin which the invention may be incorporated;

[0018]FIG. 2I shows an example optical reader of the type in which theinvention may be incorporated stationed in a scan stand;

[0019]FIG. 3 is a flow diagram illustrating operations which may beperformed by an optical reading device during execution of theinvention;

[0020]FIG. 4 is a pixel diagram corresponding to a single bar symbolillustrating one possible variation of the edge detection method of theinvention;

[0021]FIG. 5 is a pixel diagram corresponding to a multiple bar symbolillustrating a second possible variation of an edge detection method ofthe invention;

[0022]FIG. 6 is a pixel diagram corresponding to a substantially uniformwhite sheet of paper illustrating a third possible variation of an edgedetection method of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] A block diagram illustrating one type of optical reading devicein which the invention may be incorporated is described with referenceto FIG. 1.

[0024] Optical reader 10 includes an illumination assembly 20 forilluminating a target object T, such as a 1D or 2D bar code symbol, andan imaging assembly 30 for receiving an image of object T and generatingan electrical output signal indicative of the data optically encodedtherein. Illumination assembly 20 may, for example, include anillumination source assembly 22, such as one or more LEDs, together withan illuminating optics assembly 24, such as one or more reflectors, fordirecting light from light source 22 in the direction of target objectT. Illumination assembly 20 may be eliminated if ambient light levelsare certain to be high enough to allow high quality images of object Tto be taken. Imaging assembly 30 may include an image sensor 32, such asa 1D or 2D CCD, CMOS, NMOS, PMOS, CID or CMD solid state image sensor,together with an imaging optics assembly 34 for receiving and focusingan image of object T onto image sensor 32. The array-based imagingassembly shown in FIG. 1 may be replaced by a laser scanning basedimaging assembly comprising a laser source, a scanning mechanism, emitand receive optics, a photodetector and accompanying signal processingcircuitry.

[0025] Optical reader 10 of FIG. 1 also includes programmable controlunit 40 which preferably comprises an integrated circuit microprocessor42 and an application specific integrated circuit or ASIC 44. Processor42 and ASIC 44 are both programmable control devices which are able toreceive, output and process data in accordance with a stored programstored in memory unit 45 which may comprise such memory elements as aread/write random access memory or RAM 46 and an erasable read onlymemory or EROM 47. RAM 46 typically includes at least one volatilememory device but may include one or more long term non-volatile memorydevices. Processor 42 and ASIC 44 are also both connected to a commonbus 48 through which program data and working data, including addressdata, may be received and transmitted in either direction to anycircuitry that is also connected thereto. Processor 42 and ASIC 44differ from one another, however, in how they are made and how they areused.

[0026] More particularly, processor 42 is preferably a general purpose,off-the-shelf VLSI integrated circuit microprocessor which has overallcontrol of the circuitry of FIG. 2, but which devotes most of its timeto decoding image data stored in RAM 46 in accordance with program datastored in EROM 47. Processor 44, on the other hand, is preferably aspecial purpose VLSI integrated circuit, such as a programmable logic orgate array, which is programmed to devote its time to functions otherthan decoding image data, and thereby relieve processor 42 from theburden of performing these functions.

[0027] The actual division of labor between processors 42 and 44 willnaturally depend on the type of off-the-shelf microprocessors that areavailable, the type of image sensor which is used, the rate at whichimage data is output by imaging assembly 30, etc. There is nothing inprinciple, however, that requires that any particular division of laborbe made between processors 42 and 44, or even that such a division bemade at all. This is because special purpose processor 44 may beeliminated entirely if general purpose processor 42 is fast enough andpowerful enough to perform all of the functions contemplated by thepresent invention. It will, therefore, be understood that neither thenumber of processors used, nor the division of labor therebetween, is ofany fundamental significance for purposes of the present invention.

[0028] With processor architectures of the type shown in FIG. 1, atypical division of labor between processors 42 and 44 will be asfollows. Processor 42 is preferably devoted primarily to the tasks ofdecoding image data, once such data has been stored in RAM 46, handlingmenuing options and reprogramming functions, processing commands anddata received from control/data input unit 39 which may comprise suchelements as trigger 74 and keyboard 78 and providing overall systemlevel coordination. Processor 44 is preferably devoted primarily tocontrolling the image acquisition process, the A/D conversion processand the storage of image data, including the ability to access memories46 and 47 via a DMA channel. Processor 44 may also perform many timingand communication operations. Processor 44 may, for example, control theillumination of LEDs 22, the timing of image sensor 32 and ananalog-to-digital (A/D) converter 36, the transmission and reception ofdata to and from a processor external to reader 10, through an RS-232, anetwork, or a serial bus such as USB, (or other) compatible I/Ointerface 37 and the outputting of user perceptible data via an outputdevice 38, such as a beeper, a good read LED and/or a display monitorwhich may be provided by a liquid crystal display such as display 82. Inthe alternative, given that off-the-shelf microprocessors havingbuilt-in serial interfaces and display controllers are now available, itmay be convenient to configure processor 42 to control output, displayand I/O functions. Control of output, display and I/O functions may alsobe shared between processors 42 and 44, as suggested by bus driver I/Oand output/display devices 37″ and 38′ or may be duplicated, assuggested by microprocessor serial I/O ports 42A and 42B and I/O anddisplay devices 37″ and 38′. As explained earlier, the specifics of thisdivision of labor is of no significance to the present invention.

[0029]FIGS. 2A through 2H show examples of types of housings in whichthe present invention maybe incorporated. FIGS. 2A and 2B show a IDoptical reader 10-1, while FIGS. 2C-2H show 2D optical readers 10-2,10-3, 10-4. Housing 12 of each of the optical readers 10-1 through 10-4is adapted to be graspable by a human hand and has incorporated thereinat least one trigger switch 74 for activating image capture and decodingand/or image capture and character recognition operations. Readers 10-1,10-2, 10-3 include hard-wired communication links 78 for communicationwith external devices such as other data collection devices or a hostprocessor, while reader 10-4 includes an antenna 80 for providingwireless communication with an external device such as another datacollection device or a host processor.

[0030] In addition to the above elements, reader 10-3 and 10-4 eachinclude a display 82 for displaying information to a user and a keyboard78 for enabling a user to input commands and data into the reader.

[0031] Any one of the readers described with reference to FIGS. 2Athrough 2H may be mounted in a stationary position as is illustrated inFIG. 2I showing a generic optical reader 10 docked in a scan stand 90.Scan stand 90 adapts portable optical reader 10 for presentation modescanning. In a presentation mode, reader 10 is held in a stationaryposition and an indicia bearing article is moved across the field ofview of reader 10.

[0032] As will become clear from the ensuing description, the inventionneed not be incorporated in a portable optical reader. The invention mayalso be incorporated, for example, in association with a control unitfor controlling a non-portable fixed mount imaging assembly thatcaptures image data representing image information formed on articlestransported by an assembly line, or manually transported across acheckout counter at a retail point of sale location.

[0033] Now referring to particular aspects of the invention, a highlevel flow diagram illustrating operation of an optical readerconfigured to operate in accordance with the invention is shown in FIG.3. At block 102 control unit 40 analyzes image information that isgenerated by the reader's imaging assembly. At block 104 control unit 40determines if a machine readable indicia is likely represented in theimage information, and if the unit 40 at block 104 determines that amachine recognized indicia is likely contained in the image informationthen the unit at block 106 changes the mode of operation of the readingdevice.

[0034] Preferred implementations of each of these steps will now bedescribed in detail. While the analysis of image information (block 102)could be carried out by processing of analog image signals produced bysensor array 32, or by a photo detector in the case the imaging assemblyis laser based, the analysis of image information is preferably carriedout by processing of pixel image data captured by control unit 40. Inthe control system of FIG. 2, control unit 40 captures image data byrepeatedly reading the output from A/D converter 36 and writing thesedata into RAM 46. In the case of a 2D imaging assembly, pixel datacorresponding to an entire field of view of the imaging assembly istypically referred to as a “frame” of image data, or a bit map.

[0035] Control unit 40 may detect for the presence of machine readableindicia in captured image data by detecting for edge transitions oredges in the image data. An edge of an image is an area of contrastbetween a darker indicia and lighter indicia. A plain uniformlyreflecting substrate can be expected to have substantially no humanrecognizable edge transitions. A substrate having a bar code symbolformed thereon, however, can be expected to have several edgetransitions because each interface between a space and a dark area of asymbol constitutes an edge. Substrates having machine readable textcharacters formed thereon can also be expected to have several edgetransitions. In one implementation of the invention, control unit 40determines that a frame of image data captured by an imaging system islikely to contain machine recognizable indicia if the scene containsmore than a predetermined number of edge transitions.

[0036] The preferred number of predetermined edge transitions that isselected to indicate the likely presence of machine readable indicia ina captured frame of image data may vary within a wide range (from about3 to 50 or more) depending on such factors as the characteristics ofmachine readable indicia which are to be subject to image capture, andon characteristics of the image capturing process. The selection of arelatively small number of edge transitions (such as between about 5 and15) as the predetermined threshold number of edges indicating the likelypresence of machine readable indicia is useful in the case a readingdevice according to the invention is configured to detect for thepresence of bar code symbols having 50 or more edge transitions formedon a substrate that is moving relative to a reading device during imagecapture. Selecting a number of edge transitions substantially less thanthe actual number of edge transitions expected to be found in a stillcaptured image aids in the detection of machine readable indicia incaptured images that are blurred as a result of a substrate and/orreader being moved during the image capture process.

[0037] In an alternative implementation of the invention, control unit40 determines that a captured scene likely contains machine recognizableindicia if the number of edge transitions represented in captured framesof image data changes by more than a predetermined amount over thecourse of one or more consecutively captured frames. Such animplementation is useful, for example, where control unit 40 is employedto capture images from scenes having backgrounds known to have a highnumber of edges (wood grain surfaces, for example). In one specificexample of this type of implementation, control unit 40 can beconfigured to determine that a first frame is not likely to containmachine recognizable indicia if the frame has edge transitions numberingwithin an “equilibrium” range number of edge transitions and todetermine that a next frame is likely to contain machine recognizableindicia if the next frame contains a number of edge transitions thatdiffers from that of the previous frame by a predetermined amount.

[0038] Control unit 40 may detect edge transitions in captured imagedata in a variety of ways. In one method for edge detection, controlunit 40 analyzes a line of image data to determine if a captured imageincludes an edge or edges. Control unit 40 may detect edges in acaptured image by establishing at least one threshold in a line of imagedata and recording an edge detection each time the line image datacrosses the threshold. In one embodiment of the invention, the at leastone threshold may be established based on the average pixel value or ona function of the average pixel value of the line of image data.

[0039] If control unit 40 captures image data from a 1×N 1D image sensorthen the line of image or pixel data analyzed by control unit 40comprises image data generated from the row of pixels of the linearpixel array. If control unit 40 captures image data from a 1D laserscanning assembly then the line of image data analyzed by control unit40 comprises image data corresponding to a line sweep of a laserscanner. If control unit 40 captures image data from a 2D image sensorthen the line of image data analyzed by control unit 40 may comprise anyline grouping of pixels from the initial captured bit map. The line ofpixel values analyzed by control unit 40 may comprise, for example,pixel data one or more pixels wide corresponding to a vertical,horizontal, diagonal linear row of pixels from the sensor array. Theline of pixels need not be linear, however. For example, the line ofpixels analyzed by control unit 40 may comprise an arcuate or jaggedgrouping of pixels from a captured bit map. Furthermore, control unit 40need not analyze every pixel from a selected line. For example it may bebeneficial to ignore pixels (such as every other pixel) in, a given linein the interest of increasing processing speed. The line of pixel dataanalyzed by control unit 40 normally comprises pixel data captured in aninitial bit map. It will be understood, however, that a pixel value of aline of image data in accordance with the invention may not be an actualpixel value from an initial bit map, but a representative pixel valuedetermined, for example, based on the values of a grouping ofpositionally related pixels of an initial bit map.

[0040]FIG. 4 shows pixel data 108 that corresponds to a scene having asingle bar symbol. The regions of higher pixel intensity 110 and 112correspond to space while the region of lower pixel intensity 114corresponds to the bar. It is seen by threshold 116 that a singlethreshold may successfully aid in the detection of edge transitions of ascene. If edges are detected for based on pixel data crossings ofthreshold 116, then threshold 116 will result in the recording of twoedge transitions 118 and 120, which is the correct number for a scenehaving a single bar. However, it is seen by threshold 122 that ifthreshold 122 is in a range of pixel values about which pixel values mayfluctuate due to noise, that detecting for edges using a singlethreshold may yield erroneous detections of edge transitions.

[0041] Threshold 122 also illustrates other potential problems which mayarise with use of a constant valued threshold. In the case that a sceneis illuminated non-uniformly, or if indicia is formed on substratenon-uniformly, use of a constant threshold for determining edgetransitions can yield inconsistent edge detections of image datacorresponding to similar indicia. It is seen that although region 110and region 112 both correspond to a white substrate, they areilluminated slightly non-uniformly and therefore application of constantthreshold 122 would result in edges being detected for in region 110 andnot being detected in region 112.

[0042] Accordingly, in view of the potential problems involved with theuse of a single, constant threshold, it may be beneficial to detect foredges in row of pixel image data utilizing a plurality of “adaptive”thresholds. FIG. 5 illustrates thresholding edge detection methodutilizing two “adaptive” thresholds, an adaptive maximum threshold 130and an adaptive minimum threshold 132.

[0043] In an adaptive threshold, the threshold at any one pixel may be afunction of the values of pixels in proximity with that pixel. Althoughthe adaptive threshold method increases the processing load andcomputation time, use of adaptive threshold or thresholds enables anedge detection method, according to the invention, to accurately recordedge transitions in the case there is a non-uniform illumination of ascene or in the case that dark regions of machine readable indicia areformed on a substrate non-uniformly. In the specific example of FIG. 5,the maximum threshold 130 is established at a predetermined percent(such as an 80 percent level) of a tracking line, which tracks localmaximum points of the row of pixel data 138 with a provision thatresults in local maximum points being bypassed if a local maximum pointis significantly lower than neighboring local maximum points. Theminimum threshold 130, meanwhile, is established at a predeterminedpercent value (such as 20 percent above) of a minimum tracking line,which is established by tracking local minimum points of the row ofpixel data 138 with the provision that results in local minimum pointsthat are significantly higher than neighboring local minimum pointsbeing bypassed. Edge transitions in the example of FIG. 5 are recordedwhen the pixel data 138 falls below the minimum threshold 132, e.g.,point 134, and when the pixel data rises above maximum threshold 130,e.g. point 136.

[0044]FIG. 4 shows pixel data corresponding to a single bar in a scene,FIG. 5 shows pixel data corresponding to a machine readable symbol,while FIG. 6 shows pixel data corresponding to a white sheet of paper.In the example of FIG. 4 corresponding to a single bar, the edgedetection method utilizing threshold 120 will record two edges, whichaccording to the invention is not normally a sufficient number of edgesto constitute the detection of a machine readable indicia. Normally, thereader is programmed so that a substantial number of edges (normally atleast three) are required to constitute the detection of a machinereadable indicia. In the example of FIG. 5 corresponding to a machinereadable indicia then application of an edge detection method results insixteen (16) edges being detected. This is normally sufficient toconstitute the detection of a machine readable indicia.

[0045] In the edge detection methods described thus far with referenceto FIGS. 4 and 5, the detection of edges depends only on whether thereis detectable fluctuation of pixel image data and not on the magnitudeof the fluctuation. Accordingly, as the edge detection method has beendescribed thus far, application of the method may result in edges beingdetected from image data corresponding to a substantially uniform grayscale scene. It can be observed from the example of FIG. 6 illustratinga row 140 of pixel data corresponding to a substantially uniform whitesubstrate that use a single constant threshold for detecting edges oruse of maximum and minimum thresholds as described in connection withthe example of FIG. 5 would result in several edge transitions beingdetected in the pixel data.

[0046] To the end that application of the method does not result inedges being detected on a substrate having substantially uniform grayscale images therein, a pixel variance measurement step may be executed.In a pixel variance measurement step, the pixel value may be analyzed todetermine a measurement in pixel variance, such as the differencebetween the maximum and minimum pixel value, or the difference betweenthe average local minimum value and the average local maximum value. Ifthe pixel variance measurement value does not exceed a predeterminedvalue, then it is determined that the scene is one of a substantiallyuniform reflectance, and either processing ends or edges that aredetected are ignored.

[0047] In the example illustrated in FIG. 6, the step of pixel variancemeasurement is substituted for by a specialized minimum thresholdestablishing step. Specifically, in the example shown in FIG. 6, minimumthreshold 142 is established according to a rule which precludes minimumthreshold 142 from being established within a predetermined value fromthe value of maximum threshold 144 at any given pixel location. Usingthis threshold establishing step, it is seen that the pixel value 140never falls below minimum threshold 142, and that therefore no edges aredetected. This is the correct result for a substantially uniform grayscale image in which substantially no edges are humanly recognizable.

[0048] It has been mentioned that control unit 40, according to themethod of the invention, normally analyzes a line of image data at agiven time. In the case of a 1D image sensor, there is often only onepixel row from which a line of image data can be determined. However, a2D image sensor comprises several rows of pixels from which numerouslines of image data can be selected. In a preferred implementation ofthe invention in a reader having a 2D image sensor control unit 40applies several lines of image data determined from an initial bit mapto an edge detection method in succession. In one embodiment of theinvention, control unit 40 applies lines of image data corresponding toa vertical, horizontal, diagonal left, and diagonal right pixel rows toan edge detection method in succession. In another embodiment, controlunit 40 applies parallel lines of image data determined from the arrayto an edge detection method in succession. If application of an edgedetection method to any one of the lines of image data yields thedetection of an image having a plurality of edge transitions before alllines of image data determined from a given frame are applied to themethod, then program control may immediately jump to step 106 to changethe mode of operation of the reader without analyzing the remaininglines of image data.

[0049] Referring again to the flow diagram of FIG. 3, it is seen thatcontrol unit 40 proceeds to block 106 to change the mode of operation ofthe reader when the control unit determines that a machine readableindicia is in the field of view.

[0050] Normally, this change in the reader operating mode will comprisea change in the operation of the reader from a first mode, wherein thereader does not have the capability to recognize machine readableindicia to a second mode wherein the reader actively attempts torecognize machine readable indicia. The second mode of operation may becharacterized, for example, by the activation of illumination array 22,and/or by activation of a bar code decoding algorithm and/or an opticalcharacter recognition algorithm. When a bar code decoding algorithm isactivated, control unit 40 may process a frame of image data to locateimage data pertaining to a symbology, determine the identity of thatsymbology, and apply further decoding steps to the image datacorresponding to that symbology to determine the message encoded by thesymbol. The second mode of operation may also be characterized by theactivation of an optical character recognition (OCR) algorithm. When anoptical character recognition algorithm is activated, control unit 40processes image data from a frame to determine the identity of any textcharacters or other machine readable image data which may be representedin the frame. If in the second mode of operation, the reader isprogrammed either to decode a symbol or to perform OCR on other machinereadable indicia, then control unit 40 should be configured to executecertain processing steps to determine whether the detected machinereadable image data corresponds to a symbol or whether the image datacorresponds to non-symbol indicia. Since such processing steps, andspecific steps of various decoding and optical character recognitionalgorithms are well known, they will not be discussed further herein.

[0051] While this invention has been described in detail with referenceto a preferred embodiment, it should be appreciated that the presentinvention is not limited to that precise embodiment. Rather, in view ofthe present disclosure which describes the best mode for practicing theinvention, many modifications and variations would present themselves tothose skilled in the art without departing from the scope and spirit ofthis invention, as defined in the following claims.

What is claimed is:
 1. A method for operating an optical reading device,the optical reading device including an imaging assembly and a controlsystem, the method including the steps of: capturing a frame of imagingdata using the imaging assembly; applying at least one adaptivethreshold to the imaging data to obtain edge transition data; analyzingthe edge transition data to detect the presence of machine readableindicia; and changing a mode of operation of the device from a firstmode of operation to at least one second mode of operation, if the stepof analyzing indicates that the imaging data represents machine readableindicia.
 2. The method of claim 1, wherein the step of applying furthercomprises: obtaining a line of the imaging data; applying the at leastone adaptive threshold for the line of imaging data; and recording anedge transition when said image information crosses the at least oneadaptive threshold.
 3. The method of claim 2, wherein the at least oneadaptive threshold includes two adaptive thresholds.
 4. The method ofclaim 3, wherein the two adaptive thresholds includes a maximum adaptivethreshold and a minimum adaptive threshold.
 5. The method of claim 4,wherein the edge transition data indicates an edge transition when theline of imaging data crosses both the maximum adaptive threshold and theminimum adaptive threshold.
 6. The method of claim 4, wherein themaximum adaptive threshold is approximately 80% of the line.
 7. Themethod of claim 4, wherein the minimum adaptive threshold isapproximately 20% of the line.
 8. The method of claim 1, wherein the atleast one adaptive threshold is applied on a pixel-by-pixel basis, suchthat the adaptive threshold for a pixel is a function of pixel valuesproximate the pixel.
 9. The method of claim 1, wherein the step ofapplying further comprises the step of performing a pixel variancemeasurement.
 10. The method of claim 9, wherein the pixel variancemeasurement further comprises: calculating a difference between amaximum pixel value and a minimum pixel value; and comparing thedifference to a predetermined value to determine whether the imagingdata represents an edge transition.
 11. The method of claim 10, whereinan edge transition is detected if the difference is greater than thepredetermined value, and an edge transition is not detected if thedifference is less that or equal to the predetermined value.
 12. Themethod of claim 9, wherein the pixel variance measurement furthercomprises: calculating a difference between an average local maximumpixel value and an average local minimum pixel value; and comparing thedifference to a predetermined value to determine whether the imagingdata represents an edge transition.
 13. The method of claim 12, whereinan edge transition is detected if the difference is greater than thepredetermined value, and an edge transition is not detected if thedifference is less that or equal to the predetermined value.
 14. Themethod of claim 12, wherein the average local maximum pixel value andthe average local minimum pixel value are pixel values taken from a lineof imaging data.
 15. The method of claim 9, wherein the imaging datarepresents a gray scale image if the difference is less that or equal tothe predetermined value.
 16. The method of claim 1, further comprisingthe step of recording detected edge transitions when a pixel valuecrosses the at least one adaptive threshold.
 17. The method of claim 16,wherein the step of applying includes the step of setting a maximumthreshold and a minimum threshold, and wherein the recording stepincludes the step of counting an edge transition if said imageinformation rises above said maximum threshold or falls below saidminimum threshold.
 18. The method of claim 17, wherein the maximumthreshold is separated from the minimum threshold by a predeterminedvalue.
 19. The method of claim 1, wherein the optical reading device isnot configured to decode imaging data in the first mode, but isconfigured to read optical indicia in the at least one second mode. 20.The method of claim 19, wherein the optical indicia includes bar codeindicia.
 21. The method of claim 20, wherein the bar code indiciaincludes a linear bar code and/or a two-dimensional bar code.
 22. Themethod of claim 19, wherein the optical indicia is read using opticalcharacter recognition.
 23. The method of claim 1, wherein the opticalreading device is configured to provide increased illumination in the atleast one second mode.
 24. The method of claim 1, wherein the step ofchanging step further comprises: determining a number of edgetransitions in the edge transition; and changing the mode if the numberof edge transitions exceeds a predetermined amount.
 25. The method ofclaim 1, wherein the step of changing step further comprises:determining a number of edge transitions in the edge transition; andchanging the mode if the number of edge transitions changes by apredetermined amount.
 26. The method of claim 1, wherein step ofanalyzing further comprises: sequentially analyzing a plurality of linesof imaging data; and Terminating the step of analyzing if one of theplurality of lines indicates the presence of edge transitions in excessof a predetermined amount.
 27. The method of claim 1, wherein the stepof analyzing includes the step of sequentially analyzing vertical,horizontal, and diagonal rows of image information.
 28. The method ofclaim 1, wherein the step of analyzing includes the step of sequentiallyanalyzing parallel lines of image information.
 29. An optical imagingdevice for reading machine readable indicia disposed on an object, thedevice comprising: an imaging assembly configured to capture a frame ofimaging data corresponding to an image of the object; and a controlsystem coupled to the imaging assembly, the processor being configuredto, apply at least one adaptive threshold to the imaging data to therebydetect edge transitions in the imaging data, analyze the edgetransitions to determine whether the imaging data includes machinereadable indicia, and decode the machine readable indicia if the step ofanalyzing indicates the presence of machine readable indicia.
 30. Theoptical imaging device of claim 29, wherein the control system isfurther configured to change a mode of operation of the optical readerif the step of analyzing indicates the presence of machine readableindicia.
 31. The optical reading device of claim 29, wherein the controlsystem is further configured to: analyze at least one line of imageinformation from the captured frame; and change a mode of operation ofthe optical reading device if the number of edge transitions exceeds apredetermined amount.
 32. The optical reading device of claim 31,wherein the control system is configured to sequentially analyze aplurality of the lines of image information in the captured frame 33.The optical reading device of claim 29, wherein the control systemsequentially analyzes vertical, horizontal, and diagonal rows of imageinformation.
 34. The optical reading device of claim 29, wherein thecontrol system is further configured to: analyze at least one line ofimaging data; and record the edge transitions of the at least one lineof imaging data.
 35. The optical reading device of claim 34, wherein theat least one adaptive threshold includes a maximum threshold and aminimum threshold, the control system being configured to count an edgetransition if a portion of the at least one line exceeds the maximumthreshold or falls below the minimum threshold.
 36. The optical readingdevice of claim 35, wherein a value of the maximum threshold and a valueof the minimum threshold differ by a predetermined amount.
 37. Theoptical reading device of claim 29, wherein the control system isfurther configured to: analyze at least one line of image informationfrom the captured frame; and change the mode of operation of the opticalreading device if the number of the edge transitions changes by apredetermined amount.
 38. The optical reading device of claim 36,wherein the control system is further configured to sequentially analyzea plurality of lines of the captured frame.
 39. The optical readingdevice of claim 36, wherein the control system is further configured toterminate detection of the edge transitions when the number of the edgetransitions changes by a predetermined amount.
 40. The optical readingdevice of claim 29, wherein the control system is configured tosequentially analyze vertical, horizontal, and diagonal rows of imageinformation.
 41. The optical reading device of claim 29, wherein thecontrol system is further configured to analyze at least one line ofimaging data and record the edge transitions based on crossings of theline of imaging data of the at least one adaptive threshold.
 42. Theoptical reading device of claim 41, wherein the at least one adaptivethreshold includes a maximum threshold and a minimum threshold, and thecontrol system is configured to record the an edge transition if aportion of the line of imaging data exceeds the maximum threshold orfalls below the minimum threshold.
 43. The optical reading device ofclaim 42, wherein the maximum threshold and the minimum threshold areseparated by a predetermined range of values such that edge transitionsare not recorded from imaging data corresponding to a substantiallyuniform gray scale image.